PHOTOS: Epic Views of Apollo's First Moon Rover
But those studies were not conclusive, with some results showing the impact occurring as early as 30 million years after the birth of the solar system.
The new research, which favors a later date, paves the way for scientists to get on with an even meatier question: Why the big discrepancy between Earth's prolonged formation and the speedy evolution of Mars?
Analysis of Martian meteorites shows the planet formed in just a few million years, a finding supported by the new computer simulations.
That debate is likely to continue until samples are brought back from sister planet Venus, which, like Earth, likely had a long incubation.
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"There's a lot of uncertainty in what (the solar system's) proto-planetary disk looked like," lead researcher Seth Jacobson, with the Cote d'Azur Observatory in Nice, France, wrote in an email to Discovery News.
"This disk is filled with large planetary embryos and small planetesimals which collide and eventually build the planets. We don't know what shaped this disk, how fast it grew, how long it lasted .... If we could compare Earth and Venus this would tell us a lot about conditions in the proto-planetary disk," he wrote.